Autoantigenic proteins that bind recombinogenic sequences in Epstein-Barr virus and cellular DNA.

Abstract

We have identified conserved autoantigenic cellular proteins that bind to G-rich sequence motifs in recombinogenic regions of Epstein-Barr virus (EBV) DNA. This binding activity, called TRBP, recognizes the EBV terminal repeats, a locus responsible for interconversion of linear and circular EBV DNA. We found that TRBP also binds to EBV DNA sequences involved in deletion of EBNA2, a gene product required for immoralization. We show that TRBP binds sequences present in repetitive cellular DNA, such as variablenumber tandem repeats (VNTR) and immunoglobulin heavychain class switch regions. We propose that EBV utilizes cellular DNA recombination systems to mediate several types of viral genome alterations. These findings may lead to an understanding of the mechanism of rearrangements of EBV DNA that are a central feature of the biology of the virus.In this report we address the hypothesis that recombination events in Epstein-Barr virus (EBV) DNA resemble comparable cellular processes and are mediated by similar machinery. We have sought and identified an activity in cellular nuclear extracts that recognizes recombinogenic sequences in EBV and cellular DNA.The genome of EBV assumes several forms. In virions, EBV DNA is linear; in cells, during latent infection, the viral genome becomes a circular plasmid (1-3). After induction of lytic viral DNA replication a linear EBV DNA molecule is once again produced for packaging into virions (4, 5). Interconversion between the linear and circular forms of EBV DNA, an essential process of the EBV life cycle, takes place in the 538-bp terminal repeats (TRs) (see Fig. 1A). The occasional integration of EBV DNA into the cellular genome also occurs at the TRs (6, 7).Internal rearrangements and deletions are frequently present in EBV DNA molecules. Rearrangements ofEBV DNA, called heterogeneous (het) DNA are found in defective viral genomes and may lead to activation of the EBV lytic replication cycle (8). A region of the EBV genome spanning the coding regions for a portion ofthe leader protein (LP) and the entire EBV-encoded nuclear antigen 2 (EBNA2) protein is prone to deletion: viruses with LP/EBNA2 deletions are unable to immortalize lymphocytes (9). het DNA and deletions that remove the EBNA2 gene are detected in the tongue of patients with oral hairy leukoplakia, a disease characterized by unbridled EBV replication in epithelial cells (10, 11). Thus, het DNA and the EBNA2 deletions, paraphenomena of lytic EBV replication in vitro, may be important in EBV pathogenesis (12). Generation of EBV genomes with het DNA and EBNA2 deletions occurs in sequences of IR1, the 3072-bp large internal repeat (IR) (Fig. 1B) (9, 13-17 (TGGGTGG). The portion of EBV IR1 involved in the recombination with retrovirus is identical to that which participates in the EBNA2 deletion in the P3J-HR-1 EBV strain (13). Furthermore, sequences at the junction between EBV and the retrovirus were similar to G-rich sequences found in the EBV TR (20).G-rich sequences similar to those present in recombinog...

Structure and role of the terminal repeats of Epstein-Barr virus in processing and packaging of virion DNA

“…A highly conserved cellular protein has been found to bind to the termini of EBV in vitro, and its binding site spans the 11-bp element. It has been suggested that the protein is involved in such recombination processes, which remains to be demonstrated (21).…”

Epstein‐Barr Virus Infection of T Cells: Implications for Altered T‐Lymphocyte Activation, Repertoire Development and Autoimmunity

“…Failure of EBV to circularize in T cells thus appears to indicate a critical block in the progression of EBV infection to the latent program of gene expression readily demonstrated in B cells (Alfieri et al 1991). To our knowledge, there is no current description of the mechanism which EBV and other herpes viruses utilize to form the viral episome from the linear infectious form during the establisbment of latency, although some evidence suggests that EBV uses a pathway similar to the immunoglobulin class switcbing pathway for the transition from the circular to the linear form during viral reactivation (Sun et al 1994).…”

“…The DBP may also have a role in the reverse transition of the circular genome to the linear state during lytic induction of the virus (Decaussin et al 1995). Since some indirect evidence suggests that the linearization of EBV from the circular episomal form utilizes sequences similar to the sequences recognized during class switch immunoglobulin recombination (Sun et al 1994), cleavage at class switch sequences may also be a DBP function. Hence, both immunoglobulin V(D)J recombination and immunoglobulin class switching recombination may simultaneously have arisen via integration and duplication of portions of an extrachromosomal element, a coincidence previously only suspected for the origins of V(D)J recombination (reviewed in Dreyfus 1992, Thompson 1995.…”

Epstein-Barr virus induction of recombinase-activating genes RAG1 and RAG2

“…In the infected cell, EBV is maintained extrachromosomally in a circular (latent) or linear (replicating) molecular configuration (1,12,29). Recent detection in human lesions of EBV DNA rearrangement (31,39,43) and chromosomal integration (20,35) suggests that recombination events are a central feature of EBV biology and pathogenesis (41,46). Because internal rearrangements in the viral genome exhibit general sequence specificity (9,16,31,41), we questioned whether site-specific recombinases involved in diversification of the host immune response mediate DNA rearrangements in this lymphotropic virus.…”

“…Although insufficient to implicate V(D)J recombinase specifically, viral integration does indicate the presence of recombinogenic activity in RAG-positive cells. Whether increased RAG transcription correlates with a functional V(D)J recombinase or represents a more general stimulation of cellular recombination mechanisms (3,41) is the focus of ongoing studies.…”